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In another important contribution to the field, University of Pittsburgh researchers correlated PIB-PET measurements of fibrillar Aβ burden with FDG PET measurements of cerebral glucose metabolism in probable AD patients, MCI patients, and normal controls who met their criteria for PIB positivity. As predicted, the study demonstrated regional associations between higher fibrillar Aβ burden and lower cerebral glucose metabolism in PIB-positive probable AD patients. While it failed to find similar associations between fibrillar Aβ burden and glucose metabolism in PIB-positive normal controls, it would be interesting to investigate these associations in an entire cohort of cognitively normal old subjects without enrichment for PIB positivity and, when sufficient samples are available, in ApoE4 carrier versus non-carrier groups. Among other things, one might predict an association between fibrillar Aβ burden and lower glucose metabolism in certain regions, such as the posterior cingulate/precuneus region, in older adult ApoE4 carriers. The finding of regional associations between higher fibrillar Aβ burden and higher metabolism in PIB-positive MCI patients is unexpected but interesting, and the two alternative interpretations for this finding are quite reasonable if not yet compelling. The relationship between fibrillar Aβ burden and glucose metabolism (which is thought to reflect the density or activity of terminal neuronal fields) is important, and the Pittsburgh team has done a thoughtful job in characterizing this relationship in PIB-positive AD, MCI, and cognitively normal subjects.